Method and apparatus for encoding video using variable partitions for predictive encoding, and method and apparatus for decoding video using variable partitions for predictive encoding

ABSTRACT

A video encoding method and apparatus and a video decoding method and apparatus are provided. The video encoding method includes: prediction encoding in units of a coding unit as a data unit for encoding a picture, by using partitions determined based on a first partition mode and a partition level, so as to select a partition for outputting an encoding result from among the determined partitions; and encoding and outputting partition information representing a first partition mode and a partition level of the selected partition. The first partition mode represents a shape and directionality of a partition as a data unit for performing the prediction encoding on the coding unit, and the partition level represents a degree to which the coding unit is split into partitions for detailed motion prediction.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/232,156, filed on Dec. 26, 2018, which is acontinuation application of U.S. patent application Ser. No. 15/705,325,filed on Sep. 15, 2017, (now U.S. Pat. No. 10,205,942, issued Feb. 12,2019), which is a continuation application of U.S. patent applicationSer. No. 14/831,043, filed on Aug. 20, 2015, (now U.S. Pat. No.9,787,983, issued Oct. 10, 2017) which is a continuation application ofU.S. patent application Ser. No. 13/522,408, filed on Jul. 16, 2012 (nowU.S. Pat. No. 9,137,533, issued Sep. 15, 2015), which is a NationalStage application under 35 U.S.C. § 371 of PCT/KR2011/000300 filed onJan. 14, 2011, which claims the benefit of U.S. Provisional PatentApplication No. 61/295,312, filed on Jan. 15, 2010 in the U.S. Patentand Trademark Office, and claims priority from Korean Patent ApplicationNo. 10-2011-0004019, filed on Jan. 14, 2011 in the Korean IntellectualProperty Office, all the disclosures of which are incorporated herein intheir entireties by reference.

BACKGROUND 1. Field

Apparatuses and methods consistent with exemplary embodiments relate toencoding and decoding a video.

2. Description of the Related Art

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codecfor effectively encoding or decoding the high resolution or high qualityvideo content is increasing. In a related art video codec, a video isencoded according to a limited encoding method based on a macroblockhaving a predetermined size.

Video compression uses spatial correlations and temporal correlations.Generally, inter-prediction is performed in units of specific size data,for example, 16×16 macroblocks. When a macroblock having a specific sizeis split into two, four, or a greater number of motion areas andinter-prediction is then performed on each motion area, distortion of arestored image in relation to the original image may occur, and overheadfor transmitting a result of the inter prediction may be generated. Whena motion area for inter-prediction is finely split, distortion of arestored image in relation to the original image decreases, but overheadincreases. Accordingly, in inter-prediction, there is a trade-offrelationship between a distortion of a restored image in relation to theoriginal image and an overhead for transmitting an inter predictionresult.

SUMMARY

Aspects of one or more exemplary embodiments relate to video encodingand video decoding that use a partition having a variable shape and avariable size for prediction encoding.

According to an aspect of an exemplary embodiment, there is provided avideo encoding method using a variable partition, the video encodingmethod including: performing prediction encoding in units of a codingunit as a data unit for encoding a picture, by using partitionsdetermined based on a first partition mode and a partition level, so asto select a partition which is to output an encoding result from amongthe determined partitions, wherein the first partition mode represents ashape and directionality of a partition as a data unit for performingprediction encoding on the coding unit, and the partition levelrepresents a degree to which the coding unit is split into partitionsfor detailed motion prediction; and encoding and outputting partitioninformation representing a first partition mode and a partition level ofthe selected partition.

Not only a partition that is the same size as an existing macroblock, apartition that is half the size of the existing macroblock, and apartition that is quarter the size of the existing macroblock may bedetermined, but also a partition capable of predicting a change in thedirectionality and position of a texture and a detailed motion may bedetermined. Since the shape and direction of a partition that allow adetailed motion of a partition to be predicted may be adjusted based onthe size of a coding unit, prediction encoding and decoding may beperformed in sufficient consideration of image characteristics.

According to an aspect of an exemplary embodiment, there is provided avideo encoding method using a variable partition, the method including:performing prediction encoding in units of a coding unit as a data unitfor encoding a picture, by using partitions determined based on a firstpartition mode and a partition level, so as to select a partition whichis to output an encoding result from among the determined partitions,wherein the first partition mode represents a shape and directionalityof a partition as a data unit for performing prediction encoding on thecoding unit, and the partition level represents a degree to which thecoding unit is split into partitions for detailed motion prediction; andencoding and outputting partition information representing a firstpartition mode and a partition level of the selected partition.

According to an aspect of another exemplary embodiment, there isprovided a video decoding method using a variable partition, the methodincluding: extracting partition information including a first partitionmode and a partition level from a received bitstream, wherein theextracting is performed on units of a coding unit as a data unit forencoding a picture, the first partition mode represents the shape anddirectionality of a partition as a data unit for performing predictiondecoding on the coding unit, and the partition level represents a degreeto which the coding unit is split into partitions for detailed motionprediction; and restoring the picture by performing prediction decodingby using partitions determined based on the first partition mode and thepartition level of the extracted partition information.

According to an aspect of another exemplary embodiment, there isprovided a video encoding apparatus using a variable partition, theapparatus including: an encoder which performs prediction encoding inunits of a coding unit as a data unit for encoding a picture, by usingpartitions determined based on a first partition mode and a partitionlevel so as to select a partition which is to output an encoding resultfrom among the determined partitions, and encodes the picture so as todetermine an encoding mode of the coding unit, wherein the firstpartition mode represents a shape and directionality of a partition as adata unit for performing prediction encoding on the coding unit, and thepartition level represents a degree to which the coding unit is splitinto partitions for detailed motion prediction; and an output unit whichencodes and outputs partition information representing a first partitionmode and a partition level of the selected partition, information abouta prediction mode of the selected partition, and encoding informationincluding information about the encoding mode and encodes and outputs amotion vector and residual data of the selected partition.

According to an aspect of another exemplary embodiment, there isprovided a video decoding apparatus using a variable partition, theapparatus including: an extractor which extracts partition informationincluding a first partition mode, the first partition mode representinga shape and directionality of a partition as a data unit for performingprediction encoding on a coding unit as a data unit for encoding apicture, and a partition level representing a degree to which the codingunit is split into partitions for detailed motion prediction,information about a prediction mode of the partition, encodinginformation including information about the encoding mode, and a motionvector and residual data of the partition, from a received bitstream,wherein the extraction is performed for each coding unit; and a decoderwhich performs prediction decoding on partitions determined based on thefirst partition mode and the partition level of the extracted partitioninformation, based on a prediction mode of the determined partitions,and restores the picture according to the encoding mode.

According to an aspect of another exemplary embodiment, there isprovided a computer-readable recording medium having recorded thereon aprogram for executing the video encoding method.

According to an aspect of another exemplary embodiment, there isprovided a computer-readable recording medium having recorded thereon aprogram for executing the video decoding method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a video encoding apparatus using a variablepartition, according to an exemplary embodiment;

FIG. 2 is a block diagram of a video decoding apparatus using a variablepartition, according to an exemplary embodiment;

FIG. 3 is a diagram illustrating coding units having a hierarchicalstructure, according to an exemplary embodiment;

FIG. 4 illustrates partitions having a tree structure which are definedby a first partition mode and a partition level, according to anexemplary embodiment;

FIG. 5 illustrates a relationship among the first partition mode, thepartition level, and a second partition mode, according to an exemplaryembodiment;

FIG. 6 is a flowchart of a video encoding method using a variablepartition, according to an exemplary embodiment;

FIG. 7 is a flowchart of a video decoding method using a variablepartition, according to an exemplary embodiment;

FIG. 8 is a block diagram of a video encoding apparatus that uses avariable partition for prediction encoding on the basis of coding unitshaving a tree structure, according to an exemplary embodiment;

FIG. 9 is a block diagram of a video decoding apparatus that uses avariable partition for prediction encoding on the basis of coding unitshaving a tree structure, according to an exemplary embodiment;

FIG. 10 is a diagram for describing a concept of coding units accordingto an exemplary embodiment;

FIG. 11 is a block diagram of an image encoder based on coding units,according to an exemplary embodiment;

FIG. 12 is a block diagram of an image decoder based on coding units,according to an exemplary embodiment;

FIG. 13 is a diagram illustrating deeper coding units according todepths, and partitions, according to an exemplary embodiment;

FIG. 14 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 15 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 16 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 17, 18, and 19 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment;

FIG. 20 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1;

FIG. 21 is a flowchart of a video encoding method using a variablepartition based on coding units having a tree structure, according to anexemplary embodiment; and

FIG. 22 is a flowchart of a video decoding method using a variablepartition based on coding units having a tree structure, according to anexemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an ‘image’ may denote a still image for a video or a movingimage, that is, the video itself. Hereinafter, a ‘data unit’ may denotea collection of pieces of data falling within a predetermined range fromamong pieces of data of a video.

Encoding and decoding of a video by using a variable partition forprediction encoding, according to an exemplary embodiment, will now bedescribed with reference to FIGS. 1 through 7. Encoding and decoding ofa video by using a variable partition for prediction encoding on thebasis of coding units having a tree structure, according to an exemplaryembodiment, will be described below with reference to FIGS. 8 through22.

FIG. 1 is a block diagram of a video encoding apparatus 10 using avariable partition for prediction encoding, according to an exemplaryembodiment.

Referring to FIG. 1, the video encoding apparatus 10 using a variablepartition includes an encoder 11 and an output unit 12. For convenienceof explanation, the video encoding apparatus 10 using the variablepartition will hereinafter be referred to as a video encoding apparatus10.

The video encoding apparatus 10 receives a picture sequence of a video,encodes the picture sequence by performing inter-prediction,intra-prediction, transformation, quantization, and entropy encoding oneach picture of the picture sequence, and outputs encoded video data,that is, a result of the encoding, and encoding information includinginformation about an encoding mode.

The video encoding apparatus 10 may split a current picture into dataunits each having a predetermined size and perform encoding on each ofthe data units, in order to efficiently encode the current picture.Hereinafter, a data unit for encoding a picture is referred to as a‘coding unit’. The encoder 11 may determine a coding unit and anencoding method which is to be performed on each coding unit. Theencoding method determined for each coding unit is referred to as anencoding mode.

Data redundancy may occur among temporally sequential images of a videoor among spatially neighboring areas in an image of a video. Duringvideo compression encoding, a prediction encoding technique ofperforming encoding with reference to spatially/temporally neighboringdata region(s) is performed to remove data redundancy amongspatially/temporally adjacent data regions to reduce the size of encodeddata.

In the prediction encoding technique, a neighboring data region havingredundant data is searched for based on a data unit having apredetermined size and a predetermined shape, and thus a disparity (thatis, a motion) between the searched redundant data units and adifferential value (that is, a residual data) between the original andredundant data of the searched redundant data units may be encoded.

The encoder 11 may determine a partition that is a data unit whosemotion is to be compared with a motion of neighboring data, in order toperform prediction encoding on each coding unit. The size of thepartition may be smaller than or equal to that of the coding unit. Theencoder 11 may output residual data obtained by removing redundant datafrom each partition, according to prediction encoding using thedetermined partition.

The encoder 11 selects a partition for outputting an encoding result, byperforming prediction encoding using partitions that are determinedbased on first partition modes and partition levels.

The encoder 11 may perform prediction encoding on each coding unit byusing partitions having various shapes, directionalities, and sizes, andselect a partition through which residual data is to be finally outputfrom among the partitions. A directionality of a partition represents adirection in which the partition is split from a coding unit. Theencoder 11 may select a partition for prediction encoding resulting in ahighest encoding efficiency by determining and comparing encodingefficiencies according to the various partitions.

Encoding efficiency may be determined in consideration of an errorbetween original data and restored data, an overhead generated afterencoding, and the like. The encoding efficiency according to predictionencoding may be measured using Rate-Distortion Optimization based onLagrangian multipliers.

Partitions according to an exemplary embodiment may be defined based onthe first partition modes and the partition levels. A first partitionmode according to an exemplary embodiment indicates the shape anddirectionality of a partition.

For example, partition types such as a rectangular partition, a squarepartition, a non-rectangular partition, and the like may be defineddepending on the type of first partition mode. For example, thedirectionality in which a coding unit is split, for example, i)partitions into which a coding unit is halved vertically, halvedhorizontally, halved both vertically and horizontally, or diagonallysplit, ii) partitions into which a coding unit is split along a splitline biased on a left, right, upper or lower end of the coding unit, oriii) partitions obtained by splitting a coding unit from a width to afacing width, from a height to a facing height, from a width to anadjacent height, and from a height to an adjacent width, according tothe first encoding mode may be defined.

A partition level according to an exemplary embodiment denotes a degreeto which a coding unit is split into partitions for fine motionprediction. A split ratio of the width (height) of a partition to thewidth (height) of a coding unit may be determined depending on the valueof partition level.

For example, as the partition level according to an exemplary embodimentincreases, partitions obtained by finely splitting the width and heightof a coding unit may be determined. For example, partitions obtained bysplitting the width or height of a coding unit at 1:(n-1), 2:(n-2), . .. , (n-2):2, and (n-1):1 may be determined based on division of thewidth or height of the coding unit into n equal parts. In this case, nmay increase as the partition level increases.

However, a minimum size of a partition according to an exemplaryembodiment is limited, that is, a coding unit cannot be splitinfinitely. Accordingly, the upper limit, the lower limit, or both theupper and lower limits of a partition level of a partition may bedetermined based on a size of a current coding unit, which is determinedaccording to a hierarchical tree structure. The value of a partitionlevel may be limited by a system or user setting.

The widths and heights of partitions whose shapes and directions aredetermined based on the first partition mode according to an exemplaryembodiment may increase or decrease. The widths and heights of thepartitions whose shapes and directions are determined based on the firstpartition mode according to an exemplary embodiment may be definedaccording to a second partition mode. In other words, the secondpartition mode may determine detailed partition types from amongallowable partitions according to the first partition mode.

Shapes and directions of the partitions of the first partition mode aredetermined according to the first partition mode, and the width, theheight, or both the width and the height of a partition increases ordecreases to be one or more times the minimum width or minimum height ofa partition that is determined according to the partition level. Thus,the second partition mode may be defined so as to indicate each of thepartitions of the first partition mode.

For example, when the minimal width and the minimal height of apartition is determined to be 1/n of the width and height of a codingunit according to the partition level, the second partition modeindicates each of partitions into which the width or height of thecoding unit is split at 1:(n-1), 2:(n-2), . . . , (n-2):2, and (n-1):1.

Accordingly, the encoder 11 may also determine the second partition modeaccording to the first partition mode, and the types or number of secondpartition modes may be determined according to the first partition modeand the partition level.

The output unit 12 may encode and output partition informationrepresenting the first partition mode and the partition level of thepartition selected by the encoder 11. The partition information mayfurther include the second partition mode according to the firstpartition mode. The partition information may include partition levelrestriction information for determining the lower or upper limit of thepartition level.

The output unit 12 may output a motion vector and residual data of apartition that have been generated by prediction-encoding using thepartition determined by the encoder 11. The output unit 12 may alsoencode and output information about a prediction mode representing aprediction encoding method using the partition determined by the encoder11, and encoding information including information about an encodingmode. Encoding information according to an exemplary embodiment may beinserted into a sequence parameter set (SPS). The encoding informationaccording to an exemplary embodiment may be encoded in every unit ofdata units such as sequences, pictures, frames, slices, maximum codingunits, or the like, and inserted into an output bitstream.

FIG. 2 is a block diagram of a video decoding apparatus 20 using avariable partition for prediction encoding, according to an exemplaryembodiment.

Referring to FIG. 2, the video decoding apparatus 20 using a variablepartition for prediction encoding includes an extractor 21 and a decoder22. For convenience of explanation, the video decoding apparatus 20using a variable partition for prediction encoding will hereinafter bereferred to as a video decoding apparatus 20.

The video decoding apparatus 20 may receive a bitstream into which apicture sequence of a video has been encoded, and perform decodingthrough entropy decoding, dequantization, inverse transformation,inter-prediction/compensation, and intra-prediction with respect to eachencoded picture data, thereby restoring a picture.

The extractor 21 may parse the received bitstream to extract the encodedpicture data and motion vectors. The extractor 21 may parse the receivedbitstream to extract encoded residual data.

The extractor 21 may parse the received bitstream to extract encodinginformation. The extractor 21 may read information about an encodingmode, partition information, and information about a prediction modefrom the encoding information. The first partition mode and thepartition level of a partition of a coding unit may be read from thepartition information.

The partition information extracted by the extractor 21 may includeinformation regarding shapes and directions of partitions that providehighest encoding efficiency, from among the partitions having ahierarchical tree structure that are formed by the first partition modeand the partition level.

The decoder 22 may determine a partition for prediction encoding withrespect to the picture, based on the partition information extracted andread by the extractor 21. The decoder 22 may prediction-decode theencoded residual data of a partition by using the prediction mode andthe motion vector extracted by the extractor 21.

The decoder 22 may determine a partition of each coding unit, based onthe partition information. The decoder 22 may determine the shape of apartition and the directionality where a coding unit is split intopartitions, based on the first partition mode included in the partitioninformation. The decoder 22 may determine a degree to which a codingunit is finely spit into partitions, based on the partition levelincluded in the partition information.

For example, the decoder 22 may determine partition types such as arectangular partition, a square partition, a non-rectangular partition,and the like, depending on the type of first partition mode. The decoder22 may determine the directionality where a coding unit is split intopartitions, based on the first partition mode included in the partitioninformation. For example, i) partitions according to the first partitionmodes may include partitions into which a coding unit is vertically,horizontally, both vertically and horizontally, and diagonally split,ii) a partition positioned on a left, right, upper or lower end of thecoding unit, or iii) partitions obtained by splitting a coding unit froma width to a facing width, from a height to a facing height, from awidth to an adjacent height, and from a height to an adjacent width.

The decoder 22 may determine a split ratio at which the width and heightof a coding unit is split, based on the partition level. As thepartition level increases, partitions obtained by finely splitting thewidth and height of a coding unit may be determined. For example, whenpartitions into which one of the width and the height or both of thewidth and height of a coding unit is split at 1:(n-1), 2:(n-2), . . . ,(n-2):2, and (n-1):1 are determined, n may increase as the partitionlevel increases.

The upper limit, the lower limit, or both the upper and lower limits ofthe partition level of a partition may be determined based on a size ofa current coding unit, which is determined according to a hierarchicaltree structure. Information about a limit value of a partition level ina system or user setting may be extracted from the received bitstream.

The extractor 21 may also extract a second partition mode representing apartition having a predetermined width and a predetermined height fromamong the partitions whose shapes and directions are determined based onthe first partition mode, from the partition information. The decoder 22my determine partitions of each coding unit, based on the firstpartition mode information, the partition level, and the secondpartition mode information that are included in the partitioninformation.

The decoder 22 may increase or decrease the widths and heights of thepartitions whose shapes and directions are determined based on the firstpartition mode, according to the second partition mode.

Since the first partition mode may determine shape and directionality ofa partition, the partition level may determine the minimum width orminimum height of the partition, and the second partition mode mayindicate each of partitions according to the first partition mode andthe partition level, the width or height of a partition may bedetermined to be one or more times the minimum width or height of thepartition.

For example, the minimum width and the minimum height of a partition maybe determined to be 1/n of the width and height of a coding unitaccording to a partition level. The decoder 22 may determine partitionsobtained by splitting the width or height of a coding unit at 1:(n-1),2:(n-2), . . . , (n-2):2, and (n-1):1 based on a second partition mode.

The decoder 22 may perform prediction decoding on partitions determinedbased on partition information, according to a prediction mode, andrestore a picture according to an encoding mode.

The video encoding apparatus 10 and the video decoding apparatus 20 maydetermine not only a partition that is the same size as an existingmacroblock, a partition that is half the size of the existingmacroblock, and a partition that is quarter the size of the existingmacroblock, but also a partition capable of predicting a change in thedirectionality and position of a texture and a fine motion of apartition. Since the shape and direction of a partition that allow adetailed motion of a partition to be predicted may be adjusted based onthe size of a coding unit, prediction encoding and decoding may beperformed in sufficient consideration of image characteristics.

FIG. 3 is a diagram illustrating coding units 31, 32, and 33 having ahierarchical structure 30, according to an exemplary embodiment.

According to the hierarchical structure 30 of the coding units 31, 32,and 33, the coding units 31, 32, and 33 may be sequentially smaller ascoding unit levels increase from 0 to 2 by increments of 1. As the sizesof the coding units 31, 32, and 33 are sequentially greater, morevarious shapes and directions of texture components may be included inthe coding units 31, 32, and 33. A single coding unit may includedifferent motion areas corresponding to different movements occurringover time, in a video sequence. Accordingly, for more detailed andprecise prediction encoding on a coding unit, the shape, direction, andsize of a partition included in the coding unit may vary according tothe size of the coding unit.

FIG. 4 illustrates partitions having a tree structure 50 which aredefined by a first partition mode and a partition level, according to anexemplary embodiment.

The tree structure 50 may include partitions defined by the firstpartition mode and the partition level. The encoder 11 of the videoencoding apparatus 10 may perform prediction encoding on each codingunit by using all of the partitions of the tree structure 50 and thendetermine a partition having a highest encoding efficiency, and theoutput unit 12 may encode and output residual data of the determinedpartition.

The first partition mode may represent the shape and directionality of apartition, and the partition level may denote a degree to which a codingunit is split into partitions for detailed motion prediction. Partitionsmay be defined by a combination of a first partition mode and apartition level.

A partition group 49 at a partition level of 0 includes a partition set40 of a first partition mode 0, a partition set 41 of a first partitionmode 1, a partition set 42 of a first partition mode 2, a partition set43 of a first partition mode 3, a partition set 44 of a first partitionmode 4, a partition set 45 of a first partition mode 5, a partition set46 of a first partition mode 6, and a partition set 47 of a firstpartition mode 7.

The partition set 40 of the first partition mode 0 at the partitionlevel of 0 includes a partition 0 having the same size as a coding unit.

The partition set 41 of the first partition mode 1 at the partitionlevel of 0 may include rectangular partitions 0 and 1 into which acoding unit is halved horizontally. The partition set 42 of the firstpartition mode 2 at the partition level of 0 may include rectangularpartitions 0 and 1 into which a coding unit is halved vertically.

The partition set 43 of the first partition mode 3 at the partitionlevel of 0 may include rectangular partitions 0, 1, 2, and 3 into whicha coding unit is halved both horizontally and vertically, namely, isquartered.

The partition set 44 of the first partition mode 4 at the partitionlevel of 0 may include a rectangular partition 0 which is positioned onthe left upper end of a coding unit and obtained by halving the leftedge and the upper edge of the coding unit, and a non-rectangularpartition 1 corresponding to a remaining part of the coding unit.

The partition set 45 of the first partition mode 5 at the partitionlevel of 0 may include a rectangular partition 1 which is positioned onthe right upper end of a coding unit and obtained by halving the rightedge and the upper edge of the coding unit, and a non-rectangularpartition 0 corresponding to a remaining part of the coding unit.

The partition set 46 of the first partition mode 6 at the partitionlevel of 0 may include a rectangular partition 0 which is positioned onthe left lower end of a coding unit and obtained by halving the leftedge and the lower edge of the coding unit, and a non-rectangularpartition 1 corresponding to a remaining part of the coding unit.

The partition set 47 of the first partition mode 7 at the partitionlevel of 0 may include a rectangular partition 1 which is positioned onthe right lower end of a coding unit and obtained by halving the rightedge and the lower edge of the coding unit, and a non-rectangularpartition 0 corresponding to a remaining part of the coding unit.

The first partition modes 1 and 2 may define partitions that allowaccurate prediction encoding to be performed when different motionsoccur in upper and lower areas or left and right areas of a coding unit.The first partition mode 3 may define partitions that allow detailedprediction encoding to be performed when a plurality of objects or aplurality of areas exist within a coding unit and the coding unit has acomplex motion.

The first partition modes 4, 5, 6, and 7 may define partitions thatallow accurate prediction encoding to be performed with respect to areasdefined by diagonal edges of a coding unit when the diagonal edges existwithin the coding unit. However, when the first partition modes 3, 4, 5,6, and 7 are used, accurate motion prediction is possible but anoverhead increases. Thus, the first partition modes 3, 4, 5, 6, and 7may be used in consideration of a trade-off between encoding efficiencyand overhead.

Since the partition level represents a degree to which a coding unit issplit into partitions to achieve detailed motion prediction, a minimumheight or a minimum width of a partition may decrease as the partitionlevel increases.

In the tree structure 50 of the partitions, the minimum width (minimumheight) of a partition is obtained by dividing the width (height) of acoding unit by 2 to the power of a number, and the 2 to the power of anumber increases as the partition level increases.

As described above, when a partition level is 0, the height (width) of acoding unit is not split or is halved. When the partition level isincreased to be 1, the minimum height (minimum width) of a partition maybe a quarter of the height (width) of a coding unit. When the partitionlevel is increased to be 2, the minimum height (minimum width) of thepartition may be one eighth of the height (width) of the coding unit.

The size of a coding unit does not vary regardless of the value of thepartition level in the tree structure 50 of the partitions. A partitiongroup 59 at a partition level of 1 has a precision twice as high as aprecision at the partition level of 0. According to an exemplaryembodiment, the first partition mode 1 at the partition level of 0defines partitions into which the height of a coding unit is split witha precision of ½, and the first partition mode 1 at the partition levelof 1 defines partitions into which the height of a coding unit is splitwith a precision of ¼. The first partition mode 1 at the partition levelof 2 defines partitions into which the height of a coding unit is splitwith a precision of ⅛.

In a single first partition mode, partitions of the same shape may berepeated between partition levels. For example, in the first partitionmodes 3, 4, 5, 6, and 7, the partition sets 43, 44, 45, 46, and 47 atthe partition level of 0 have the same shapes as partition sets 53 e, 54e, 55 e, 56 e, and 57 e at the partition level of 1, respectively. Inthe first partition modes 1 and 2, partition sets 51 a and 51 b at thepartition level of 1 have the same shapes as partition sets 61 b and 61e at the partition level of 2, respectively, and partition sets 52 a and52 b at the partition level of 1 have the same shapes as partition sets62 b and 62 e at the partition level of 2, respectively.

When partitions determined based on an identical first partition modeand different partition levels have the same shape, only partitions at alower partition level from among the determined partitions may be usedduring prediction encoding. For example, in the first partition mode 3,since the partition set 53 e at the partition level of 1 has the sameshape as the partition set 43 at the partition level of 0, only thepartition set 43 of the first partition mode 3 at the partition level of0, which is lower than the partition level of 1, may be used duringactual prediction encoding, and only partition information representingthe partition set 43 may be encoded. In this case, partition informationfor representing the partition set 53 e is not defined.

The partition sets 51 a and 51 b of the first partition mode 1 at thepartition level of 1 may include rectangular partitions 0 and 1 intowhich a coding unit is horizontally split at 1:3 and 3:1, respectively.The partition sets 52 a and 52 b of the first partition mode 2 at thepartition level of 1 may include rectangular partitions 0 and 1 intowhich a coding unit is vertically split at 1:3 and 3:1, respectively.

Each of the partition sets 53 a, 53 b, 53 c, 53 d, 53 e, 53 f, 53 g, 53h, and 53 i of the first partition mode 3 at the partition level of 1may include 4 rectangular partitions 0, 1, 2, and 3 into which a codingunit is split horizontally and vertically so that at least one of thehorizontal splitting and the vertical splitting is performed at 1:3,2:2, or 3:1. However, in the first partition mode 3, the partition set53 e at the partition level of 1 duplicates the partition set 43 at thepartition level of 0 and thus may not be used during predictionencoding. Partition information representing the partition set 53 e ofthe first partition mode 3 at the partition level of 1 may not bedefined.

Each of the partition sets 54 a, 54 b, 54 c, 54 d, 54 e, 54 f, 54 g, 54h, and 54 i of the first partition mode 4 at the partition level of 1may include a rectangular partition 0 which is positioned on the leftupper end of a coding unit and obtained by splitting at least one of theleft and upper edges of the coding unit at 1:3, 2:2, or 3:1, and anon-rectangular partition 1 which is a remaining part of the codingunit. However, in the first partition mode 4, the partition set 54 e atthe partition level of 1 duplicates the partition set 44 at thepartition level of 0 and thus may not be used during predictionencoding. In the partition level of 1, partition informationrepresenting the partition set 54 e of the first partition mode 4 maynot be defined.

Each of the partition sets 55 a, 55 b, 55 c, 55 d, 55 e, 55 f, 55 g, 55h, and 55 i of the first partition mode 5 at the partition level of 1may include a rectangular partition 1 which is positioned on the rightupper end of a coding unit and obtained by splitting at least one of theright and upper edges of the coding unit at 1:3, 2:2, or 3:1, and anon-rectangular partition 0 which is a remaining part of the codingunit. However, in the first partition mode 5, the partition set 55 e atthe partition level of 1 duplicates the partition set 45 at thepartition level of 0 and thus may not be used during predictionencoding. In the partition level of 1, partition informationrepresenting the partition set 55 e of the first partition mode 5 maynot be defined.

Each of the partition sets 56 a, 56 b, 56 c, 56 d, 56 e, 56 f, 56 g, 56h, and 56 i of the first partition mode 6 at the partition level of 1may include a rectangular partition 0 which is positioned on the leftlower end of a coding unit and obtained by splitting at least one of theleft and lower edges of the coding unit at 1:3, 2:2, or 3:1, and anon-rectangular partition 1 which is a remaining part of the codingunit. However, in the first partition mode 6, the partition set 56 e atthe partition level of 1 duplicates the partition set 46 at thepartition level of 0 and thus may not be used during predictionencoding. In the partition level of 1, partition informationrepresenting the partition set 56 e of the first partition mode 6 maynot be defined.

Each of the partition sets 57 a, 57 b, 57 c, 57 d, 57 e, 57 f, 57 g, 57h, and 57 i of the first partition mode 7 at the partition level of 1may include a rectangular partition 1 which is positioned on the rightlower end of a coding unit and obtained by splitting at least one of theright and lower edges of the coding unit at 1:3, 2:2, or 3:1, and anon-rectangular partition 0 which is a remaining part of the codingunit. However, in the first partition mode 7, the partition set 57 e atthe partition level of 1 duplicates the partition set 47 at thepartition level of 0 and thus may not be used during predictionencoding. In the partition level of 1, partition informationrepresenting the partition set 57 e of the first partition mode 7 maynot be defined.

Similarly, partition sets 61 a, 61 b, 61 c, 61 d, 61 e, and 61 f of thefirst partition mode 1 at the partition level of 2 may includerectangular partitions 0 and 1 into which a coding unit is horizontallysplit at 1:7, 2:6, 3:5, 5:3, 6:2, and 7:1, respectively. However, in thefirst partition mode 1, since the partition sets 61 b and 61 e at thepartition level of 2 duplicate the partition sets 51 a and 51 b at thepartition level of 1, respectively, information representing thepartition sets 61 b and 61 e of the first partition mode 1 at thepartition level of 2 may not be defined. The partition sets 62 a, 62 b,62 c, 62 d, 62 e, and 62 f of the first partition mode 2 at thepartition level of 2 may include rectangular partitions 0 and 1 intowhich a coding unit is vertically split at 1:7, 2:6, 3:5, 5:3, 6:2, and7:1, respectively. However, in the first partition mode 1, since thepartition sets 62 b and 62 e at the partition level of 2 duplicate thepartition sets 52 a and 52 b at the partition level of 1, respectively,information representing the partition sets 62 b and 62 e of the firstpartition mode 1 at the partition level of 2 may not be defined.

Although partitions of the first partition modes 3, 4, 5, 6, and 7 atthe partition level of 2 are not illustrated in FIG. 4 on account ofspace considerations, 4 rectangular partitions into which a coding unitis split horizontally and vertically so that at least one of thehorizontal splitting and the vertical splitting is performed at 1:7,2:6, 3:5, 4:4, 5:3, 6:2, or 7:1 may be defined in the first partitionmode 3 at the partition level of 2.

In the first partition mode 4 at the partition level of 2, a rectangularpartition which is positioned on the left upper end of a coding unit andobtained by splitting at least one of the left and upper edges of thecoding unit at 1:7, 2:6, 3:5, 4:4, 5:3, 6:2, or 7:1, and anon-rectangular partition corresponding to a remaining part of thecoding unit may be defined.

In the first partition mode 5 at the partition level of 2, a rectangularpartition which is positioned on the right upper end of a coding unitand obtained by splitting at least one of the right and upper edges ofthe coding unit at 1:7, 2:6, 3:5, 4:4, 5:3, 6:2, or 7:1, and anon-rectangular partition corresponding to a remaining part of thecoding unit may be defined.

In the first partition mode 6 at the partition level of 2, a rectangularpartition which is positioned on the left lower end of a coding unit andobtained by splitting at least one of the left and lower edges of thecoding unit at 1:7, 2:6, 3:5, 4:4, 5:3, 6:2, or 7:1, and anon-rectangular partition corresponding to a remaining part of thecoding unit may be defined.

In the first partition mode 7 at the partition level of 2, a rectangularpartition which is positioned on the right lower end of a coding unitand obtained by splitting at least one of the right and lower edges ofthe coding unit at 1:7, 2:6, 3:5, 4:4, 5:3, 6:2, or 7:1, and anon-rectangular partition corresponding to a remaining part of thecoding unit may be defined.

When the size of a coding unit to be encoded is sufficiently large, apartition set may be expanded to partition levels 3 and 4.

Accordingly, in the tree structure 50 of the partitions, the shape anddirectionality of a partition may be determined based on a firstpartition mode, and the minimum width and the minimum height of thepartition may be determined based on a partition level. Rectangularpartitions determined based on the first partition mode and thepartition level may include partitions each having a partition widthdouble the minimum width and a partition height double the minimumheight. In this case, a second partition mode may indicate a partitionhaving a predetermined width or a predetermined height from amongpartitions determined based on the first partition mode and thepartition level.

When a single coding unit includes two or more partitions and the widthor height of a partition 0 is determined, the width or height of theremaining partition is determined based on the width or height of thepartition 0. Thus, only the width or height of the partition 0 will nowbe discussed for convenience of explanation.

For example, in the tree structure 50 of partitions, the partitions 51 aand 51 b of the first partition mode 1 at the partition level of 1 areeach determined to have a minimum height that is a quarter of the heightof a coding unit. The heights of the partitions 51 a and 51 b of thefirst partition mode 1 at the partition level of 1 are the same as andthree times the minimum height of each of the partitions 51 a and 51 b,respectively. In this case, the second partition mode may be defined soas to indicate each of the partitions 51 a and 51 b of the firstpartition mode 1 at the partition level of 1.

Similarly, in the first partition mode 4 at the partition level of 1,the minimum width and the minimum height of a rectangular partition maybe determined to be ¼ the width and height of a coding unit, and arectangular partition 0 positioned on the left upper end of the codingunit and a non-regular partition 1 corresponding to the remaining partof the coding unit may both be formed. The second partition mode of thefirst partition mode 4 at the partition level of 1 may be defined toindicate each of the partitions 54 a, 54 b, 54 c, 54 d, 54 f, 54 g, 54h, and 54 i, which are determined with a variation of at least one ofthe width and height of a partition to one time, two times, or threetimes the minimum value of the partition. As described above, thepartition 54 e at the partition level of 1 may not be used in the firstpartition mode 4.

However, the second partition mode does not need to be separatelydefined at the partition level of 0. As a partition type that may existaccording to a first partition mode or a partition level varies, thenumber of second partition modes, the range thereof, and the like mayvary.

The video encoding apparatus 10 may perform prediction encoding based onvarious shapes, directions, and sizes of partitions by determining onepartition from among the partitions of the tree structure 50. In atrade-off between the accuracy and calculation speed of predictionencoding in the video encoding apparatus 10, when the calculation speedis more important than the accuracy, the video encoding apparatus 10 mayrestrict a selection range of first partition modes, partition levels,or second partition modes of the partitions included in the treestructure 50.

The video encoding apparatus 10 may encode partition information such asthe first partition mode, the partition level, and the second partitionmode of each partition while encoding prediction mode information, amotion vector, and residual data of each partition. Accordingly, thevideo decoding apparatus 20 may determine a partition according toextracted partition information and perform prediction decoding by usingthe determined partition.

A minimal size of partition according to an exemplary embodiment may bea partition into which a minimum coding unit is quartered. Although thesize of the partition according to an exemplary embodiment may bedetermined based on a partition level, the size is to be equal to orgreater than the minimal size of the partition and smaller than or equalto a coding unit. Thus, the size of the partition depends on the size ofthe coding unit. Accordingly, the partition level may also depend on thesize of the coding unit.

The area of a coding unit having a small size uses a partition forpredicting a motion of a small area of the coding unit. However, as acoding unit becomes larger, not only a motion of a large area of thecoding unit, but also a motion of a small area thereof may occur withinthe area of the coding unit. Thus, a coding unit having a large size isto undergo prediction encoding that uses not only large partitions, butalso small partitions. Accordingly, a partition level may also bedetermined based on the size of a coding unit.

Thus, a relationship between the size of a coding unit according to anexemplary embodiment and a definable partition level is expressed inTable 1 below.

TABLE 1 Size of partition partition partition partition partition codingunit level = 0 level = 1 level = 2 level = 3 level = 4 128 × 128 ∘ ∘ ∘ ∘∘ 64 × 64 ∘ ∘ ∘ ∘ x 32 × 32 ∘ ∘ ∘ x x 16 × 16 ∘ ∘ x x x 8 × 8 ∘ x x x x

Accordingly, only partitions having a partition level of 0, which is thelowest level, may be determined for an 8×8 coding unit. Partitionshaving partition levels of 0 and 1 may be determined for a 16×16 codingunit. Partitions having partition levels of 0 through 2, partitionshaving partition levels of 0 through 3, and partitions having partitionlevels of 0 through 4 may be determined for 32×32, 64×64, and 128×128coding units, respectively. Therefore, a partition level may be variablyallowed based on the size of a coding unit.

FIG. 5 illustrates a relationship among the first partition mode, thepartition level, and the second partition mode, according to anexemplary embodiment. In other words, the shapes of the first and secondpartition modes definable according to partition levels may bedetermined using points existing within coding units 71, 72, and 73shown in FIG. 5.

In FIG. 5, lines within the coding units 71, 72, and 73 may serve asheight or width edges of the partitions included in the coding units 71,72, and 73, and dots therewithin may denote intersecting points wherethe width and height edges of a partition meet. For example, whenstraight lines are drawn from a predetermined intersecting point withinthe coding units 71, 72, and 73 to width or height edges of the codingunits 71, 72, and 73 along the lines within the coding units 71, 72, and73, partitions into which the coding units 71, 72, and 73 are split maybe formed.

For example, at the partition level of 0, the lines within the codingunit 71 are lines that halve the width or height edge of the coding unit71. A single intersecting point may be formed by the lines within thecoding unit 71 intersecting with each other, and partitions surroundedby straight lines extending from the intersecting point to two of theleft, right, upper, and lower edges of the coding unit 71 may bedetermined. In other words, the intersecting point of the lines withinthe coding unit 71 may be the vertex of each of the determinedpartitions. Accordingly, in each first partition mode at the partitionlevel of 0, only one set of partitions may be defined within the codingunit 71. Since only one set of partitions is defined for each firstpartition mode, no second partition modes may be set.

At the partition level of 1, the lines within the coding unit 72 arelines that quarter the width or height edges of the coding unit 72.Although 9 partition vertexes may be generated by the lines with thecoding unit 72 intersecting with each other, partitions may be generatedbased on 8 vertexes exclusive of a center intersecting point (whiteintersecting point) overlapping with the intersecting point at thepartition level of 0. Accordingly, in each first partition mode at thepartition level of 1, 8 partition sets may be defined within the codingunit 72.

Similarly, at the partition level of 2, the lines within the coding unit73 are lines that split the width or height edges of the coding unit 73into eight parts. Although 49 partition vertexes may be generated by thelines within the coding unit 73 intersecting with each other, partitionsmay be generated based on 40 vertexes exclusive of 9 intersecting points(white intersecting points) overlapping with the intersecting points atthe partition levels of 0 and 1. Accordingly, in each first partitionmode at the partition level of 2, 40 partition sets may be defined inthe coding unit 73.

Accordingly, depending on the value of a partition level, the number ofsecond partition modes included in a single first partition mode maycorrespond to the number of vertexes.

FIG. 6 is a flowchart of a video encoding method using a variablepartition for prediction encoding, according to an exemplary embodiment.

In operation 81, prediction encoding is performed on each coding unit,which is a data unit for encoding a picture, by using partitions definedbased on a first partition mode and a partition level, therebydetermining a partition through which an encoding result is output.

The shape and splitting directionality of a partition may be determinedbased on the first partition mode, and the minimum width or the minimumheight of the partition may be determined based on the partition level.A partition having highest encoding efficiency may be determined fromthe defined partitions by comparing results of prediction encoding onthe defined partitions with one another, and residual data of thedetermined partition may be encoded.

An allowed range of partition levels may be determined based on the sizeof a coding unit. A second partition mode for indicating a partitionhaving a predetermined width and a predetermined height may be furtherdetermined according to the first partition mode. An allowed range ofthe number of second partition modes may be determined based on thefirst partition mode and the partition level.

In operation 82, partition information representing the first partitionmode and the partition level of the partition determined in operation 81is encoded and output. The partition information may further include thesecond partition mode, depending on the first partition mode. A motionvector and residual data of each partition may be encoded and output.Encoding information including partition information and informationabout a prediction mode and an encoding mode may be encoded and output.

FIG. 7 is a flowchart of a video decoding method using a variablepartition for prediction encoding, according to an exemplary embodiment.

In operation 91, partition information representing a first partitionmode and a partition level of a partition of each coding unit isextracted from a received bitstream. A motion vector and residual dataof each partition may be extracted by parsing the received bitstream.Encoding information including partition information and informationabout a prediction mode and an encoding mode may be extracted by parsingthe received bitstream.

In operation 92, prediction decoding is performed using partitionsdetermined based on the first partition modes and the partition levelsof the partition information extracted in operation 91, therebyrestoring a picture. The first partition modes and the partition levelsmay be read from the partition information, and second partition modesmay be read according to the first partition modes. The shape andsplitting directionality of a partition may be determined based on afirst partition mode, and the width or height of the partition inrelation to the width or height of a coding unit may be determined basedon the partition level. The residual data of each partition may bedecoded to restore a picture.

Encoding and decoding of a video by using a variable partition forprediction encoding on the basis of coding units having a treestructure, according to an exemplary embodiment, will now be describedwith reference to FIGS. 8 through 22.

FIG. 8 is a block diagram of a video encoding apparatus that uses avariable partition for prediction encoding on the basis of coding unitshaving a tree structure, according to an exemplary embodiment.

A video encoding apparatus 100 using a combination of data units on thebasis of coding units having a tree structure, according to an exemplaryembodiment, includes a maximum coding unit splitter 110, a coding unitdeterminer 120, and an output unit 130. For convenience of explanation,the video encoding apparatus 100 using the combination of data units onthe basis of the coding units having a tree structure will hereinafterbe shortened to a video encoding apparatus 100.

The maximum coding unit splitter 110 may split a current picture basedon at least one maximum coding unit for the current picture of an image.If the current picture is larger than the maximum coding unit, imagedata of the current picture may be split into the at least one maximumcoding unit. The maximum coding unit according to an exemplaryembodiment may be a data unit having a size of 32×32, 64×64, 128×128,256×256, etc., wherein a shape of the data unit may be a square having awidth and length in squares of 2. The image data may be output to thecoding unit determiner 120 according to the at least one maximum codingunit.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes a number of times thecoding unit is spatially split from the maximum coding unit, and as thedepth deepens, deeper encoding units according to depths may be splitfrom the maximum coding unit to a minimum coding unit. A depth of themaximum coding unit is an uppermost depth and a depth of the minimumcoding unit is a lowermost depth. Since a size of a coding unitcorresponding to each depth decreases as the depth of the maximum codingunit deepens, a coding unit corresponding to an upper depth may includea plurality of coding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an exemplary embodiment is split according to depths, theimage data of a spatial domain included in the maximum coding unit maybe hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split, may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. Thus, the encoded image data of the coding unitcorresponding to the determined coded depth is finally output. Also, thecoding units corresponding to the coded depth may be regarded as encodedcoding units.

The determined coded depth and the encoded image data according to thedetermined coded depth are output to the output unit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to the same depthin one maximum coding unit, it is determined whether to split each ofthe coding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the image data is split to regions according to the depthsand the encoding errors may differ according to regions in the onemaximum coding unit, and thus the coded depths may differ according toregions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be divided according to coding units of at least onecoded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an exemplary embodiment mayinclude coding units corresponding to a depth determined to be the codeddepth, from among all deeper coding units included in the maximum codingunit. A coding unit of a coded depth may be hierarchically determinedaccording to depths in the same region of the maximum coding unit, andmay be independently determined in different regions. Similarly, a codeddepth in a current region may be independently determined from a codeddepth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of splitting times from a maximum coding unit to a minimumcoding unit. A first maximum depth according to an exemplary embodimentmay denote the total number of splitting times from the maximum codingunit to the minimum coding unit. A second maximum depth according to anexemplary embodiment may denote the total number of depth levels fromthe maximum coding unit to the minimum coding unit. For example, when adepth of the maximum coding unit is 0, a depth of a coding unit, inwhich the maximum coding unit is split once, may be set to 1, and adepth of a coding unit, in which the maximum coding unit is split twice,may be set to 2. Here, if the minimum coding unit is a coding unit inwhich the maximum coding unit is split four times, 5 depth levels ofdepths 0, 1, 2, 3, and 4 exist, and thus the first maximum depth may beset to 4, and the second maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit. Examples of transformation performed for video encodingaccording to an exemplary embodiment may include frequencytransformation, orthogonal transformation, integer transformation, andthe like.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the transformation is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may variously select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split to coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea prediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, a size of apartition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partition typeinclude symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

The prediction unit according to an exemplary embodiment may include thepartitions described above with reference to FIGS. 1 through 7. In otherwords, the shape and splitting directionality of a prediction unit maybe determined based on a first partition mode according to an exemplaryembodiment, and a ratio of the size of the prediction unit to the sizeof a coding unit may be determined based on the value of partitionlevel. An allowed range of the partition level, that is, the upper orlower limit of the partition level, may be determined according to thesize of the coding unit.

A second partition mode for representing the type of detailed partitionmay be determined according to the first partition mode.

The video encoding apparatus 100 may perform prediction encoding byusing prediction units having a tree structure on the basis ofhierarchical relationships between first partition modes and betweenpartition levels, and compare results of the prediction encoding withone another, thereby determining a partition having highest encodingefficiency. The video encoding apparatus 100 may determine a partitionof a first partition mode and a partition level that provide highestencoding efficiency, for each coding unit.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit.

In order to perform the transformation in the coding unit, thetransformation may be performed based on a transformation unit having asize smaller than or equal to the coding unit. For example, thetransformation unit may include a transformation unit for an intra modeand a transformation unit for an inter mode.

Similarly to the coding unit based on the tree structure according to anexemplary embodiment, the transformation unit in the coding unit may berecursively split into smaller sized regions, and thus residual data inthe coding unit may be divided according to the transformation havingthe tree structure according to transformation depths.

A transformation depth indicating the number of splitting times to reachthe transformation unit by splitting the height and width of the codingunit may also be set in the transformation unit. For example, in acurrent coding unit of 2N×2N, a transformation depth may be 0 when thesize of a transformation unit is also 2N×2N, may be 1 when each of theheight and width of the current coding unit is split into two equalparts, totally split into 41 transformation units, and the size of thetransformation unit is thus N×N, and may be 2 when each of the heightand width of the current coding unit is split into four equal parts,totally split into 42 transformation units and the size of thetransformation unit is thus N/2×N/2. For example, the transformationunit may be set according to a hierarchical tree structure, in which atransformation unit of an upper transformation depth is split into fourtransformation units of a lower transformation depth according to thehierarchical characteristics of a transformation depth.

Similarly to the coding unit, the transformation unit in the coding unitmay be recursively split into smaller sized regions, so that thetransformation unit may be determined independently in units of regions.Thus, residual data in the coding unit may be divided according to thetransformation having the tree structure according to transformationdepths.

Encoding information according to coding units corresponding to a codeddepth uses not only information about the coded depth, but alsoinformation related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit anda method of determining a partition, according to exemplary embodiments,will be described in detail below with reference to FIGS. 11 and 12.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an exemplary embodiment is a rectangulardata unit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. Alternatively, the minimum unit may be a maximumrectangular data unit that may be included in all of the coding units,prediction units, partition units, and transformation units included inthe maximum coding unit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to coding units,and encoding information according to prediction units. The encodinginformation according to the coding units may include the informationabout the prediction mode and about the size of the partitions. Theencoding information according to the prediction units may includeinformation about an estimated direction of an inter mode, about areference image index of the inter mode, about a motion vector, about achroma component of an intra mode, and about an interpolation method ofthe intra mode. Also, information about a maximum size of the codingunit defined according to pictures, slices, or GOPs, and informationabout a maximum depth may be inserted into a header of a bitstream.

When the prediction unit is determined based on the first partitionmode, the partition level, and the like described above with referenceto FIGS. 1 through 7, the output unit 130 may encode and outputpartition information including the first partition mode and thepartition level of a partition to serve as encoding information. Theoutput unit 130 may also encode a motion vector and residual data inunits of prediction units and output a result of the encoding.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit of thecurrent depth having the size of 2N×2N may include maximum 4 of thecoding unit of the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

In addition, since the type of prediction units and partitions intowhich a coding unit is split may vary based on diverse sizes of codingunits and also vary based on the first partition mode, the partitionlevel, the second partition mode, and the like, prediction encodingbased on the image characteristics included in the coding unit may beperformed.

FIG. 9 is a block diagram of a video decoding apparatus that uses avariable partition for prediction encoding on the basis of coding unitshaving a tree structure, according to an exemplary embodiment.

A video decoding apparatus 200 using a combination of data units on thebasis of coding units having a tree structure, according to an exemplaryembodiment, includes a receiver 210, an image data and encodinginformation extractor 220, and an image data decoder 230. Forconvenience of explanation, the video decoding apparatus 200 using thecombination of data units on the basis of the coding units having a treestructure will hereinafter be shortened to a video decoding apparatus200.

Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for various operations of the video decoding apparatus200 are identical to those described with reference to FIG. 8 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture or SPS.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, encodinginformation about the coded depth and the encoding mode according to anexemplary embodiment may further include combination-related informationabout a current prediction unit or a current partition.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. The predetermined data units to which the same information aboutthe coded depth and the encoding mode is assigned may be inferred to bethe data units included in the same maximum coding unit.

The information about the encoding mode according to an exemplaryembodiment may include partition information that includes the firstpartition mode and the partition level.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include a predictionincluding intra prediction and motion compensation, and an inversetransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

The image data decoder 230 may read the partition information from amongthe information about the encoding mode and determine a partitiondefined based on the first partition mode and the partition level fromamong the partition information. The image data decoder 230 maydetermine the shape and splitting directionality of a prediction unit onthe basis of a first partition mode according to an exemplaryembodiment, and determine a ratio of the size of the prediction unit tothe size of a coding unit on the basis of the value of partition level.According to the first partition mode, the image data decoder 230 maydetermine a partition in consideration of the second partition mode forrepresenting the type of detailed partitions.

The first partition mode, the partition level, and the second partitionmode according to an embodiment may define a partition determined tohave highest encoding efficiency by performing prediction encoding byusing prediction units having a tree structure on the basis ofhierarchical relationships between first partition modes and betweenpartition levels and comparing results of the prediction encoding withone another during an encoding process. The image data decoder 230 mayperform prediction decoding by using a partition of a first partitionmode and a partition level that provide highest encoding efficiency, foreach coding unit.

Also, the image data decoder 230 may read the information about atransformation unit based on a tree structure, including the informationabout the size of the transformation unit of the coding unit accordingto coded depths, and perform inverse transformation based on atransformation unit in units of a coding unit, so as to perform theinverse transformation according to maximum coding units.

The image data decoder 230 may determine at least one coded depth of acurrent maximum coding unit by using split information according todepths. If the split information indicates that image data is no longersplit in the current depth, the current depth is a coded depth.Accordingly, the image data decoder 230 may decode encoded data of atleast one coding unit corresponding to the each coded depth in thecurrent maximum coding unit by using the information about the partitiontype of the prediction unit, the prediction mode, and the size of thetransformation unit for each coding unit corresponding to the codeddepth, and output the image data of the current maximum coding unit.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode.

The video decoding apparatus 200 may obtain encoding information aboutat least one coding unit that generates the minimum encoding error whenencoding is recursively performed for each maximum coding unit, and mayuse the information to decode the current picture. In other words, thecoding units having the tree structure determined to be the optimumcoding units in each maximum coding unit may be decoded.

The video decoding apparatus 200 extracts and reads partitioninformation about a method of determining a partition through comparisonbetween the results of prediction encoding with respect to theprediction units having a tree structure, and performs predictiondecoding by using the partition information, thereby enabling accuratedecoding.

A method of determining coding units having a tree structure, aprediction unit, and a transformation unit, according to an exemplaryembodiment, will now be described with reference to FIGS. 10 through 20.

FIG. 10 is a diagram for describing a concept of coding units accordingto an exemplary embodiment.

A size of a coding unit may be expressed in width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth denotes atotal number of splits from a maximum coding unit to a minimum decodingunit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havingthe higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two layers by splitting the maximum coding unittwice. Meanwhile, since the maximum depth of the video data 330 is 1,coding units 335 of the video data 330 may include a maximum coding unithaving a long axis size of 16, and coding units having a long axis sizeof 8 since depths are deepened to one layer by splitting the maximumcoding unit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 layers by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

FIG. 11 is a block diagram of an image encoder 400 based on codingunits, according to an exemplary embodiment.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 perform inter estimation and motioncompensation on coding units in an inter mode from among the currentframe 405 by using the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough an inverse quantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a loopfiltering unit 490. The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490, perform operations based on each codingunit from among coding units having a tree structure while consideringthe maximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

FIG. 12 is a block diagram of an image decoder 500 based on codingunits, according to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data that ispost-processed through the deblocking unit 570 and the loop filteringunit 580 may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 performoperations based on coding units having a tree structure for eachmaximum coding unit.

Specifically, the intra prediction 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

FIG. 13 is a diagram illustrating deeper coding units according todepths, and partitions, according to an exemplary embodiment.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units so as to consider characteristics of animage. A maximum height, a maximum width, and a maximum depth of codingunits may be adaptively determined according to the characteristics ofthe image, or may be differently set by a user. Sizes of deeper codingunits according to depths may be determined according to thepredetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. The maximum depthdenotes a total number of splits from a maximum coding unit to a minimumdecoding unit. Since a depth deepens along a vertical axis of thehierarchical structure 600, a height and a width of the deeper codingunit are each split. Also, a prediction unit and partitions, which arebases for prediction encoding of each deeper coding unit, are shownalong a horizontal axis of the hierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, a coding unit 640having a size of 8×8 and a depth of 3, and a coding unit 650 having asize of 4×4 and a depth of 4 exist. The coding unit 650 having the sizeof 4×4 and the depth of 4 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the encoding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition 620 having a size of 32×32, partitions622 having a size of 32×16, partitions 624 having a size of 16×32, andpartitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

The coding unit 650 having the size of 4×4 and the depth of 4 is theminimum coding unit and a coding unit of the lowermost depth. Aprediction unit of the coding unit 650 is only assigned to a partitionhaving a size of 4×4. Partitions 652 having a size of 4×2, partitions654 having a size of 2×4, and partitions 656 having a size of 2×2 mayalso be used.

Since the partitions shown in FIG. 13 have shapes obtained by halving atleast one of the height and width of the coding units corresponding tothe partitions, the partitions of FIG. 13 may correspond to thepartition sets 40, 41, 42, and 43 of the first partition modes 0, 1, 2,and 3 at the partition level of 0 described above with reference toFIGS. 1 through 7. For example, the partitions 610, 620, 630, 640, and650 may correspond to the partition set 40 of the first partition mode 0at the partition level of 0, and the partitions 612, 622, 632, 642, and652 may correspond to the partition set 41 of the first partition mode 1at the partition level of 0. The partitions 614, 624, 634, 644, and 654may correspond to the partition set 42 of the first partition mode 2 atthe partition level of 0, and the partitions 616, 626, 636, 646, and 656may correspond to the partition set 43 of the first partition mode 3 atthe partition level of 0.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 14 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an exemplary embodiment.

The video encoding apparatus 100 or 200 encodes or decodes an imageaccording to coding units having sizes smaller than or equal to amaximum coding unit for each maximum coding unit. Sizes oftransformation units for transformation during encoding may be selectedbased on data units that are not larger than a corresponding codingunit.

For example, in the video encoding apparatus 100 or 200, if a size ofthe coding unit 710 is 64×64, transformation may be performed by usingthe transformation units 720 having a size of 32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 15 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second intra transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit.

The information 800 may include partition information as the informationabout the encoding mode according to an exemplary embodiment. Forexample, the information 800 may include a partition type determinedbased on first partition mode information, a partition level, and asecond partition mode information.

FIG. 16 is a diagram of deeper coding units according to depths,according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, a partition type 916 having a size of N_0×2N_0, and apartition type 918 having a size of N_0×N_0. FIG. 16 only illustratesthe partition types 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition type is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, twopartitions having a size of N_0×2N_0, and four partitions having a sizeof N_0×N_0, according to each partition type. The prediction encoding inan intra mode and an inter mode may be performed on the partitionshaving the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. Theprediction encoding in a skip mode is performed only on the partitionhaving the size of 2N_0×2N_0.

Errors of encoding including the prediction encoding in the partitiontypes 912 through 918 are compared, and the least encoding error isdetermined among the partition types. If an encoding error is smallestin one of the partition types 912 through 916, the prediction unit 910may not be split into a lower depth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_0×N_0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, a partition type 946 having a size ofN_1×2N_1, and a partition type 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_2×N_2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d-1, and split information maybe encoded as up to when a depth is one of 0 to d-2. In other words,when encoding is performed up to when the depth is d-1 after a codingunit corresponding to a depth of d-2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d-1 and a size of 2N_(d-1)×2N_(d-1) may include partitions of apartition type 992 having a size of 2N_(d-1)×2N_(d-1), a partition type994 having a size of 2N_(d-1)×N_(d-1), a partition type 996 having asize of N_(d-1)×2N_(d-1), and a partition type 998 having a size ofN_(d-1)×N_(d-1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d-1)×2N_(d-1), two partitions having a size of2N_(d-1)×N_(d-1), two partitions having a size of N_(d-1)×2N_(d-1), fourpartitions having a size of N_(d-1)×N_(d-1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d-1) having a depth of d-1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d-1and a partition type of the current maximum coding unit 900 may bedetermined to be N_(d-1)×N_(d-1). Also, since the maximum depth is d anda minimum coding unit 980 having a lowermost depth of d-1 is no longersplit to a lower depth, split information for the minimum coding unit980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an exemplary embodiment may be arectangular data unit obtained by splitting a minimum coding unit 980 by4. By performing the encoding repeatedly, the video encoding apparatus100 may select a depth having the least encoding error by comparingencoding errors according to depths of the coding unit 900 to determinea coded depth, and set a corresponding partition type and a predictionmode as an encoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 17 through 19 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition types in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitiontypes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition type of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 2 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 2 Split Information 0 (Encoding on Coding Unit having Size of 2N ×2N and Current Depth of d) Size of Transformation Unit Split SplitPartition Type Information 0 Information 1 Symmetrical Asymmetrical ofof Prediction Partition Partition Transformation Transformation SplitMode Type Type Unit Unit Information 1 Intra 2N × 2N 2N × nU 2N × 2N N ×N Repeatedly Inter 2N × N 2N × nD (Symmetrical Encode Skip N × 2N nL ×2N Type) Coding (Only N × N nR × 2N N/2 × N/2 Units 2N × 2N)(Asymmetrical having Type) Lower Depth of d + 1

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

Referring to the partitions having a tree structure of FIG. 4, theasymmetrical partition types having sizes of 2N×nU and 2N×nD maycorrespond to the partition sets 51 a and 51 b of the first partitionmode 1 at the partition level of 1, and the asymmetrical partition typeshaving sizes of nL×2N and nR×2N may correspond to the partition sets 52a and 52 b of the first partition mode 2 at the partition level of 1.The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 20 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

Such a partition type may correspond to some of the partitions shown inFIG. 4. For example, the partition type 1322 having a size of 2N×2N maycorrespond to the partition set 40 (the first partition mode 0 at thepartition level of 0). The partition type 1324 having a size of 2N×N andthe partition type 1326 having a size of N×2N may respectivelycorrespond to the partition sets 41 and 42 (the first partition modes 1and 2 at the partition level of 0, respectively). The partition type1328 having a size of N×N may correspond to the partition set 43 (thefirst partition mode 3 at the partition level of 0). The partition type1332 having a size of 2N×nU and the partition type 1334 having a size of2N×nD may respectively correspond to the partition sets 51 a and 51 b(both the first partition mode 1 at the partition level of 1). Thepartition type 1336 having a size of nL×2N and the partition type 1338having a size of nR×2N may respectively correspond to the partition sets52 a and 52 b (both the first partition mode 2 at the partition level of1). Split information (TU size flag) of a transformation unit is a sortof a transformation index, and the size of a transformation unitcorresponding to the transformation index may vary according to theprediction unit type or partition type of the coding unit.

For example, when the partition type is set to be symmetrical, i.e. thepartition type 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if the TU size flag of a transformationunit is 0, and a transformation unit 1344 having a size of N×N is set ifa TU size flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

The TU size flag described above with reference to FIG. 18 is a flaghaving a value or 0 or 1, but the TU size flag is not limited to 1 bit,and a transformation unit may be hierarchically split having a treestructure while the TU size flag increases from 0. The TU size flag of atransformation unit may be used as an exemplary embodiment of thetransformation index.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an exemplary embodiment, together with a maximum size andminimum size of the transformation unit. According to an exemplaryembodiment, the video encoding apparatus 100 is capable of encodingmaximum transformation unit size information, minimum transformationunit size information, and a maximum TU size flag. The result ofencoding the maximum transformation unit size information, the minimumtransformation unit size information, and the maximum TU size flag maybe inserted into an SPS. According to an exemplary embodiment, the videodecoding apparatus 200 may decode video by using the maximumtransformation unit size information, the minimum transformation unitsize information, and the maximum TU size flag.

For example, if the size of a current coding unit is 64×64 and a maximumtransformation unit size is 32×32, then the size of a transformationunit may be 32×32 when a TU size flag is 0, may be 16×16 when the TUsize flag is 1, and may be 8×8 when the TU size flag is 2.

As another example, if the size of the current coding unit is 32×32 anda minimum transformation unit size is 32×32, then the size of thetransformation unit may be 32×32 when the TU size flag is 0. Here, theTU size flag cannot be set to a value other than 0, since the size ofthe transformation unit cannot be less than 32×32.

As another example, if the size of the current coding unit is 64×64 anda maximum TU size flag is 1, then the TU size flag may be 0 or 1. Here,the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizeIndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):CurrMinTuSize=max(MinTransformSize,RootTuSize/(2{circumflex over( )}MaxTransformSizeIndex))  (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2{circumflex over ( )}MaxTransformSizeIndex)’ denotesa transformation unit size when the transformation unit size‘RootTuSize’, when the TU size flag is 0, is split a number of timescorresponding to the maximum TU size flag, and ‘MinTransformSize’denotes a minimum transformation size. Thus, a smaller value from among‘RootTuSize/(2{circumflex over ( )}MaxTransformSizeIndex)’ and‘MinTransformSize’ may be the current minimum transformation unit size‘CurrMinTuSize’ that can be determined in the current coding unit.

According to an exemplary embodiment, the maximum transformation unitsize RootTuSize may vary according to the type of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.RootTuSize=min(MaxTransformSize,PUSize)  (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0, may bea smaller value from among the maximum transformation unit size and thecurrent prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.RootTuSize=min(MaxTransformSize,PartitionSize)  (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and another exemplary embodiment is not limited thereto.

The prediction unit or partitions described above with reference toFIGS. 10 through 20 are used as only partitions of the partition modes0, 1, 2, and 3 at the partition level of 0 and the first partition modes1 and 2 at the partition level of 1 in the tree structure 50 ofpartitions of FIG. 4. According to a system circumference and setting,the upper limits of the partition level and the first partition mode maybe selectively limited. The partition levels and the first partitionmodes shown in FIGS. 10 through 20 are only an embodiment, so the ideaof the present invention is not limited thereto.

FIG. 21 is a flowchart of a video encoding method using a variablepartition for prediction encoding on the basis of coding units having atree structure, according to an exemplary embodiment.

In operation 1210, a current picture of a video may be split intomaximum coding units. In operation 1220, image data of each maximumcoding unit of the current picture is encoded in units of deeper codingunits. Prediction encoding using partitions having a tree structure,which are based on first partition modes and partition levels, may beperformed in units of a coding unit, and thus a partition or predictionunit having highest prediction encoding efficiency may be determined. Adepth having highest encoding efficiency while including predictionerror may be selected as an coding depth, and coding units having thedepth determined as the encoding depth and having a tree structure maybe determined.

In operation 1230, residual data and a motion vector of each maximumcoding unit may be encoded based on the coding units having the treestructure, prediction units, or partitions. Partition informationincluding first partition modes, partition levels, and the like fordetermining a prediction unit may be encoded together with informationabout a coding depth, a prediction mode, and an encoding mode, and maybe output as encoding information.

FIG. 22 is a flowchart of a video decoding method using a variablepartition for prediction encoding on the basis of coding units having atree structure, according to an exemplary embodiment.

In operation 1310, a bitstream for an encoded video is received andparsed. In operation 1320, information about a coding depth and anencoding mode of each maximum coding unit is extracted from the parsedbitstream according to coding units having a tree structure. Partitioninformation according to an exemplary embodiment from among theinformation about a coding depth and an encoding mode may be extracted.The partition information may include first partition modes andpartition levels and may further include second partition modesaccording to the first partition modes. Encoded residual data and motionvector may be extracted in units of prediction units.

In operation 1330, coding units having a tree structure may bedetermined in units of maximum coding units, based on the informationabout a coding depth and an encoding mode, prediction units andpartitions may be determined based on the partition information, andprediction decoding may be performed on the prediction units and thepartitions. The shapes, splitting directionalities, and sizes ofprediction units and partitions into which a coding unit is split may bedetermined based on the first partition information and the partitionlevels included in the partition information. A picture may be restoreby decoding residual data of each prediction unit and each partition byusing prediction mode information and motion vectors.

The video encoding apparatus 100 may perform prediction encoding onprediction units (partitions) of various sizes, various shapes, andvarious prediction modes having a tree structure on the basis of thevariable sizes of coding units having a tree structure and compareresults of the prediction encoding with one another, thereby determininga prediction unit (partition) having highest encoding efficiency.Therefore, prediction encoding considering the characteristics of animage within a coding unit that is variable according to the size of thecoding unit may be possible.

Moreover, since information about factors that determine predictionunits used for prediction encoding is encoded and transmitted, the videodecoding apparatus 200 may guarantee accurate restoration.

Exemplary embodiments can be written as computer programs and can beimplemented in general-use digital computers that execute the programsusing a computer readable recording medium. Examples of the computerreadable recording medium include magnetic storage media (e.g., ROM,floppy disks, hard disks, etc.) and optical recording media (e.g.,CD-ROMs, or DVDs).

While exemplary embodiments have been particularly shown and describedabove, it will be understood by those of ordinary skill in the art thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the inventive concept as definedby the appended claims. The exemplary embodiments should be consideredin a descriptive sense only and not for purposes of limitation.Therefore, the scope of the invention is defined not by the detaileddescription of exemplary embodiments, but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

What is claimed is:
 1. An apparatus for decoding a video, the apparatuscomprising: a receiver configured to receive a bitstream includinginformation about a size of a maximum coding unit, and splitinformation; and a decoder configured to split a picture into aplurality of maximum coding units using the information about the sizeof the maximum coding unit, hierarchically split the maximum coding unitinto one or more coding units based on the split information, determineone or more prediction units in a coding unit among the one or morecoding units using partition type information, wherein the partitiontype information is determined based on a size of the coding unit andindicates one of a symmetric type and an asymmetric type partitioning ofthe one or more prediction units, wherein the decoder determines one ormore transform units in the coding unit, performs prediction on aprediction unit among the one or more prediction units in the codingunit and performs inverse-transformation on the one or more transformunits in the coding unit, and generates a reconstructed coding unitbased on the prediction and the inverse-transformation, and wherein thepartition type information indicates the one of the symmetric type andthe asymmetric type when a size of the coding unit is larger than apredetermined size.
 2. An apparatus for encoding a video, the apparatuscomprising: an encoder configured to split a picture into a plurality ofmaximum coding units, hierarchically split a maximum coding unit intoone or more coding units, determine one or more prediction units in acoding unit among the one or more coding units, determine one or moretransform units in the coding unit, perform prediction on a predictionunit among the one or more prediction units in the coding unit andinverse-transformation on the one or more transform units in the codingunit, and generate a reconstructed coding unit based on the predictionand the inverse-transformation; and an outputter configured to generatea bitstream including data of the picture, information about a size ofthe maximum coding unit, partition type information of the coding unit,and split information of the coding unit, wherein the partition typeinformation is determined based on a size of the coding unit andindicates one of a symmetric type and an asymmetric type partitioning ofthe one or more prediction units, and wherein the partition typeinformation indicates the one of the symmetric type and the asymmetrictype when a size of the coding unit is larger than a predetermined size.3. A non-transitory computer-readable medium for storing data associatedwith a video, comprising a bitstream stored in the non-transitorycomputer-readable medium, the bitstream including: split information ofa coding unit for hierarchically splitting a maximum coding unit among aplurality of maximum coding units into one of more coding units, whereinthe split information indicates whether a coding unit of depth k, wherek is integer, is split into coding units of depth k+1, information abouta size of a maximum coding unit for splitting a picture into theplurality of maximum coding units, a last significant coefficient flagindicating whether a non-zero effective transformation coefficient is alast non-zero effective transformation coefficient for a transformationresidual block, and partition type information of the coding unit,wherein the partition type information is determined based on a size ofthe coding unit among the one or more coding units and indicates one ofa symmetric type and an asymmetric type partitioning of one or moreprediction units in the coding unit.